The references provided herein are not admitted to be prior art to the claimed invention.
Certain cells in the body respond not only to chemical signals, but also to ions such as extracellular calcium ions (Ca.sup.2+). Extracellular Ca.sup.2+ is under tight homeostatic control and regulates various processes such as blood clotting, nerve and muscle excitability, and proper bone formation.
Calcium receptor proteins enable certain specialized cells to respond to changes in extracellular Ca.sup.2+, concentration. For example, extracellular Ca.sup.2+ inhibits the secretion of parathyroid hormone (PTH) from parathyroid cells, inhibits bone resorption by osteoclasts, and stimulates secretion of calcitonin from C-cells.
PTH is the principal endocrine factor regulating Ca.sup.2+ homeostasis in the blood and extracellular fluids. PTH, by acting on bone and kidney cells, increases the level of Ca.sup.2+ in the blood. This increase in extracellular Ca.sup.2+, then acts as a negative feedback signal, depressing PTH secretion. The reciprocal relationship between extracellular Ca.sup.2+ and PTH secretion forms an important mechanism maintaining bodily Ca.sup.2+ homeostasis.
Extracellular Ca.sup.2+ acts directly on parathyroid cells to regulate PTH secretion. The existence of a parathyroid cell surface protein which detects changes in extracellular Ca.sup.2+ has been confirmed. (Brown et al., Nature 366:574, 1993.) In parathyroid cells, this protein, the calcium receptor, acts as a receptor for extracellular Ca.sup.2+, detects changes in the ion concentration of extracellular Ca.sup.2+, and initiates a functional cellular response, PTH secretion.
Extracellular Ca.sup.2+ can exert effects on different cell functions, reviewed in Nemeth et al., Cell Calcium 11:319, 1990. The role of extracellular Ca.sup.2+ in parafollicular (C-cells) and parathyroid cells is discussed in Nemeth, Cell Calcium 11:323, 1990. These cells were shown to express similar calcium receptors. (See Brown et al., Nature 366:574, 1993; Mithal et al., J. Bone Miner. Res. 9, Suppl. 1, s282, 1994; Rogers et al., J. Bone Miner. Res. 9, Suppl, 1, s409, 1994; Garrett et al., Endocrinology 136:5202-5211, 1995.)
The ability of various molecules to mimic extracellular Ca.sup.2+ in vitro is discussed in references such as Nemeth et al., in "Calcium-Binding Proteins in Health and Disease," 1987, Academic Press, Inc., pp. 33-35; Brown et al., Endocrinology 128:3047, 1991; Chen et al., J. Bone Miner. Res. 5:581, 1990; and Zaidi et al., Biochem. Biophys. Res. Commun. 167:807, 1990.
Nemeth et al., PCT/US92/07175, International Publication Number WO 93/04373, Nemeth et al., PCT/US93/01642, International Publication Number WO 94/18959, and Nemeth et al., PCT/US94/12117, International Publication Number WO 95/11211, describe various compounds which can modulate the effect of an inorganic ion receptor.